Phase change memories (PRAM, PCM), resistance change memories (RRAM, ReRAM), magnetoresistive memories (MRAM), etc., are proposed as nonvolatile semiconductor memory devices. Each of these memories is a semiconductor memory device which uses resistance change memory elements.
A semiconductor memory device using resistance change memory elements executes writing and reading by passing current through the resistance change memory elements. Therefore, if transistors and bit lines vary in resistance, a voltage drop will occur, and thus the voltage applied to every resistance change memory element and the current which flows into every resistance change memory element will change. As a result, it will be difficult to suitably perform read operation and write operation.
Provision of read only transistors in addition to the usual select transistors may avoid the above mentioned problem, but two transistors per memory cell will be needed in this case. This means that the cell size per memory cell will be large. Therefore, a semiconductor memory device that not only achieves reduction in transistor count per memory cell but also suitably performs both read operation and write operation is desired.